Polyamide fibers (generally referred to as nylon) are preferred fibers for use as pile fibers in carpets, and are used for this purpose both in the form of continuous filament yarns, generally bulked continuous filament yarns, and in various forms as cut fiber, often called staple fiber. For many years, both nylon 66 and nylon 6 have been used in large quantities in carpeting; each polymer has its advantages, for certain purposes; as will be noted herein, nylon 6 has a greater affinity for many dyestuffs than does nylon 66. Although there are many different types of nylon carpeting, a conventional type is manufactured by inserting, e.g., plied nylon yarn into a conventional primary backing, e.g., of jute or polypropylene fibers, and then, after dyeing, applying a conventional carpet backing adhesive composition, sometimes referred to as latex, which is adhered also to a secondary backing material, as described, e.g., for a conventional tufted nylon carpet in Ucci, U.S. Pat. No. 4,579,762, issued Apr. 1, 1986. Another type of secondary backing that is frequently used is a foam backing, i.e. a layer of, e.g., polyurethane foam that can be attached directly to the primary backing without any need for such adhesive. Generally, especially when using carpeting on flooring, in addition to such primary backing, (any adhesive composition) and secondary backing (all underneath the nylon fiber pile), most householders install a conventional underlay or underpad of felted fibers or foam, e.g. of polyurethane, which conventional underlay is generally an entirely separate layer that is not integrally or overall attached to the carpet per se in the same way as the adhesive backing and secondary backing are integrally attached to the primary backing (carrying the nylon pile that is the top or outer surface of the carpet). During commercial manufacture, when such carpets are dyed, the dyeing process is carried out on the nylon pile when it is attached to the primary backing only, i.e., before (any adhesive latex composition and) the secondary backing is secured to the primary backing, and the dyeing process is carried out in conventional manner, e.g., in a beck dyeing machine, generally by a continuous process in which this primary carpet (i.e., the nylon pile and the primary backing only) is immersed in the dye liquor at the boil so as to effect contact and effective and rapid penetration of the dyestuff into the nylon pile, although there are other methods of coloring nylon, e.g., by producer-dyeing, i.e., including pigmentation into the nylon polymer before spinning.
Recently, there has been major commercial interest in imparting "stain-resistance" to nylon fibers and carpets, as described, for instance, in Textile Month, Oct., 1987, pages 32-34, and several patents are being published on various aspects of imparting stain-resistance to nylon carpets and/or carpet fibers. A major concern of the customer is the durability of the treatment during the various types of treatment that may be encountered during the life of a carpet.
Munk et al., U.S. Pat. No. 4,699,812, issued Oct. 13, 1987, claims a process for imparting stain-resistance to polyamide, wool and silk fibers by contacting the fibers with a solution of an aliphatic sulfonic acid under specified conditions of acid pH and temperature. The primary interest appears to be nylon carpets, but the procedure in, e.g., Example 1 shows vigorous mechanical agitation of a woven nylon 6 fiber "sleeve", in an aqueous solution of a commercial aliphatic sulfonic acid, at a pH adjusted to 2, and at a temperature of 50.degree. C., for 15 minutes, followed by drying with paper towels and in an oven. Variants may be used, at a manufacturing stage prior to the finished product, such as is often done in carpet manufacture; immersing the fabrics, removing excess solution by passing through rollers, and air-drying of the moist fibers at ambient temperature is mentioned; spraying onto the carpet is also mentioned; in particular, the treatment may be during or immediately subsequent the dyeing stage (column 4). Example VII shows that treatment at a pH of 3.8 shows far less improvement in stain resistance than treatment at a pH of 2. Accordingly, a pH between about 1.5 and about 3.0 is said to give more effective results (column 3, lines 56-7). Example III shows that the stain resistance (of Example I) remains after vigorous agitation for 15 minutes at 50.degree. C. in an aqueous detergent solution at a pH of 9.5, rinsing and oven-drying.
Blyth et al., U.S. Pat. No. 4,680,212, issued July 14, 1987, discloses a process of applying a spin finish to nylon fibers during the melt polymerization process by which the fibers are prepared, the finish containing one or more stain blocker(s) in specified amounts. Stain blockers are described and distinguished from fluorochemicals that are used to reduce the tendency of soil to adhere to the fiber. Fluorochemicals are used, however, in combination with a stain-blocker, to improve the durability of stain-resistance imparted by the stain-blocker, in the sense that the carpet retains more stain-resistance after being subjected to much traffic.
Blyth et al., U.S. Pat. No. 4,592,940, issued June 3, 1986, discloses a process of immersing a carpet in a boiling aqueous solution of a selected phenol-formaldehyde condensation product at an acid pH (4.5 or less). The durability of treated carpets is tested variously, including by subjecting carpet samples to two wash cycles in a heavy-duty washing machine using detergent before applying the stain.
Ucci, U.S. Pat. No. 4,579,762, issued Apr. 1, 1986, is referred to above, and claims a carpet having a primary backing coated with an adhesive composition (containing a fluorochemical) and with a pile of nylon fibers (the nylon polymer being modified to contain aromatic sulfonate units). In other words, the stain-resistance is obtained by incorporating stain-resistance into the nylon polymer itself, by chemical modification. The vulnerability of the typical carpet system to water, and the problems caused by the slow process of drying are emphasized in the lower portion of column 1, and at the top of column 2.
Ucci et al., U.S. Pat. No. 4,501,591, issued Feb. 26, 1985, claims a process for imparting stain-resistance during a process for continuously dyeing a carpet, involving adding a silicate and a sulfonated phenol- or napthol-formaldehyde condensation product to the aqueous dye liquor at specified liquor ratios, and then subjecting the carpet to an atmosphere of steam, washing with water and drying. The pH of the liquor in the only Example is 4.5, but is said typically to be in the range of 4.5 to 8 (column 3, lines 22-3). Durability is tested by carrying out a Stain Resistance Test on 5 cm .times.5 cm carpet samples alternating with heavy duty cleaning using Streamex (Steamex) commercial units. Ucci, like others, disparages (column 1, lines 46-59) the prior usage of fluorochemicals to minimize staining.
Greschler et al., EP Al 0235989, published Sep. 9, 1987, and corresponding to U.S. Pat. No. 4,780,099, discloses a process for applying sulfonated phenol- or naphthol-formaldehyde condensation products to nylon carpets, after dyeing, in a bath at a pH of between 1 and 2.5, whereby yellowing of the treated articles due to exposure to NO.sub.2 is reduced.
Mesitol NBS is mentioned by Greschler as a commercially available material (available from Mobay Chemical Corporation). This is stated in Product Bulletin T.D.S #1246/1 (Revised) August, 1981, to be an anionic after treating agent and a reserving agent to minimize the staining by selected direct dyes of the polyamide portion in polyamide cellulosic fiber blends, and the "Application Procedures" indicate that the fabric should be treated in a bath. It is understood that stain-blockers are dye-resists or dye-reserving agents such as have long been known and widely used in textile applications, such as resist-printing of nylon fibers. In other words, the mechanism of stain-blocking (in the sense of dye reserving) has been used for many years.
As indicated in the above patent specifications, and in the analysis in the Oct. 19, 1987, issue of Textile Month, referred to above, hitherto, the emphasis on process techniques, as regards imparting stain-resistance, has been reported to achieve this during the dyeing of the primary carpet, or earlier in the manufacturing process, e.g., by incorporation of modifiers into the nylon polymer, or by engineering or treatment of the fiber itself. So far as is known, prior to the present invention, it had not been disclosed that a significant improvement in stain-resistance could be effective when applied to "in place" carpet that had already been installed with any appropriate secondary backing, and normally also an underpad, as opposed to conventional immersion of the primary carpet in a dye liquor or equivalent application, usually under acid conditions, followed by conventional processing, such as washing, fixing, squeezing, and appropriate drying treatments at elevated temperatures during a manufacturing process.